The present invention relates to a method of attaching a thermocouple to a metal surface. More particularly, the present invention relates to a method of attaching a thermocouple enclosed in a metal sheath to a surface of a metal member which is particularly applicable for the attachment of a thermocouple to the inner surface of a nuclear reactor vessel which is underwater and from a remote location.
As a result of constant bombardment by gamma radiation during use, the metal of a nuclear reactor vessel, and in particular the copper in the welds, tends to lose its ductility over a period of time and to become brittle. This presents a problem of possible cracks resulting in the nuclear reactor vessel, particularly when cold water is suddenly introduced into the cooling system as a result of a malfunction which results in a sudden shut down of the system. It is therefore desireable to periodically subject the reactor vessel to an annealing process, wherein the reactor vessel is heated to a specific temperature over a specificied period of time, in order to return the desired ductility to the metal of the nuclear reactor vessel. To perform this annealing process, the vessel is opened, the contects are removed, and an annealing heater is installed in the interior of the vessel. Because of the existence of an extremely high radiation level in a reactor vessel which requires annealing, the vessel is normally submerged in water so as to significantly reduce the exposure to radiation by personnel during the operations involved in the installation of the annealing heater unit.
To monitor the temperature of the surface of the reactor vessel during the annealing process, it is necessary to distribute a plurality of thermocouples over the inner surface of the reactor vessel. As it is known, the most accurate method of measuring the temperature of a body is to either weld thermocouples to the surface of the body or to place them in thermowells, i.e. drilled holes in the surface. However, because of the extremely high radiation levels which exist in a reactor vessel which requires annealing, direct access to enable the hands-on welding of thermocouples to the inner surface of the reactor vessel is not practical and any welding process must be able to be initiated or actuated from a remote location. Moreover, the drilling of thermowells in the wall of a reactor vessel is not acceptable. Finally, the fact that the reactor vessel, and particularly the inner surface of the vessel to which the thermocouples are to be attached, is underwater presents still a further problem to be solved.